Can the anatomy of abnormal flowers elucidate relationships of the androecial members in the ginger (Zingiberaceae)?

Correlation between Inflorescence Architecture and Floral Asymmetry-Evidence from Aberrant Flowers in Canna L. (Cannaceae)

Floral symmetry studies often focus on the development of monosymmetric and polysymmetric flowers, whereas asymmetric flowers and their position and function within the inflorescence structure are largely neglected. Cannaceae is one of the few families that possesses truly asymmetric flowers, serving as a model to study the characters and mechanisms involved in the development of floral asymmetry and its context within the developing and mature inflorescence. In this study, inflorescence structure and floral morphology of normal asymmetric flowers and 16 aberrant flower collections from Canna indica L. and C. glauca L. were photographed, analyzed, and compared with attention to stamen petaloidy, floral symmetry, and inflorescence branching patterns anterior and posterior to the aberrant flower. In comparison with normal flowers, the aberrant flowers are arranged into abnormal partial florescences, and vary in floral symmetry, orientation, and degree of androecial petaloidy. The appendage of the fertile stamen is universally located distal from the higher order bract, indicating an underlying influence of inflorescence architecture. A synthetic model is proposed to explain the relationship between floral symmetry and inflorescence structure. Data from the observation of aberrant phenotypes strongly support the hypothesis that irregular petaloidy of the stamens is correlated with an asymmetric morphogenetic field within the inflorescence that contributes to the overall floral asymmetry in Canna flowers.

Asymmetric expression patterns of B- and C-class MADS-box genes correspond to the asymmetrically specified androecial identities of Canna indica

Canna indica is a common ornamental plant with asymmetric flowers having colourful petaloid staminodes. The only fertile stamen comprises a one-theca anther and a petaloid appendage and represents the lowest stamen number in the order Zingiberales. The molecular mechanism for the asymmetric androecial petaloidy remains poorly understood. Here, we studied the identity specification in Canna stamen. We observed four types of abnormal flower in terms of androecium identity transformation and analysed the corresponding floral symmetry changes. We further tested the expression patterns of B- and C-class MADS-box genes using in situ hybridization in normal Canna stamen. Homeotic conversions in the androecium were accompanied by floral symmetry changes, and the asymmetric stamen is key in contributing to the floral asymmetry. Both B- and C-class genes exhibited higher expression levels in the anther primordium than in other androecial parts. This asymmetric expression pattern precisely corresponded to the asymmetric identities of the Canna androecium. We identified C. indica as a model species for studying androecial organ identity and floral symmetry synthetically in Zingiberales. We hypothesized that homeotic genes specify floral organ identity in a putative dose-dependent manner. The results add to the current understanding of organ identity-related floral symmetry.